More than 100,000 people marched through Spain's capital and other cities Sunday calling for Israel to announce an immediate cease-fire in Gaza.
The protest in Madrid was the largest of demonstrations across Europe expressing both support and opposition for the Israeli offensive in Gaza.
Protesters filled downtown boulevards carrying banners saying "Peace," "SOS Gaza," placards with the word "Gaza" above a red-stained hand and mock blood-spattered bodies of children.
Oscar-winning actor Javier Bardem's mother Pilar, also an actress, was among speakers who addressed the crowd.
"The Spanish government has to do something. The Gaza Strip is now practically a concentration camp," she said.
Spain, which was largely an Islamic nation for 800 years until the beginning of the 16th century, has a Muslim community of around 800,000 out of a 46.1 million population.
Rallies held elsewhere in Spain
The organizers, which included the Socialist Party and trade unions, estimated turnout at 250,000. But police declined to give a figure. Rallies were held elsewhere in Spain, including Seville in the southwest and Ourense in the northwest.
"It is my duty to call on Israel to implement an immediate cease-fire," Prime Minister Jose Luis Rodriguez Zapatero told the protest in Ourense.
In Brussels, police clashed with protesters during a protest against the Israeli offensive. A march down the Belgian capital's main boulevard turned violent when some protesters overturned cars and smashed shop windows.
Police used water cannons to break up the rioting and arrested around 10 people. Police said 30,000 people marched in Brussels. Some protesters burned an Israeli flag.
Children carrying effigies of dead and bloodied babies were at the head of the procession.
In Antwerp, home to a large Hassidic Jewish community, around 800 people took part in a peaceful pro-Israel demonstration.
In London's Trafalgar Square, around 4,000 demonstrators called for an end to Hamas rocket attacks on Israel and voiced support for Israeli attempts to protect the country's citizens.
"The basic, simple goal of the people of Israel is to be allowed to live in peace, without violence, without fear, and without terror," Israeli Ambassador Ron Prosor told crowds gathered in the British capital.
British Jews speak out
But in a letter published in The Observer newspaper, 11 leading British Jews said Sunday that Israel's government must end its military action to achieve security.
"We are concerned that rather than bringing security to Israel, a continued military offensive could strengthen extremists, destabilize the region and exacerbate tensions inside Israel with its 1 million Arab citizens," their letter said.
A few thousand people in Italy marched in pro-Palestinian rallies in Rome, Naples and Verona.
A total of more than 3,000 people joined protests in support of Israel in the German cities of Frankfurt, Munich and Berlin.
In Athens, dozens of children and their parents, carrying effigies and photos of bloodied children, marched in the Greek capital to protest the Israeli operations in Gaza.